Combine bread flour with all dough ingredients except butter and knead.

Add butter to the dough and knead again until smooth.

Let the dough rise for 15 minutes (first proofing).

Mash the sweet potatoes and mix with sugar and heavy cream to make the filling.

Roll out the proofed dough with a rolling pin.

Spread the sweet potato filling evenly over the dough.

Fold the dough over the filling.

Cut the folded dough into strips using a scraper.

Twist each strip into a spiral shape.

Let the twisted dough rise for 40 minutes (second proofing).

Brush the twists with egg wash and sprinkle black sesame seeds on top.